Combichrist has a lot of songs that would make good themes for the Chaos Gods.

Khorne: God Bless http://www.youtube.com/watch?v=v5vpHgARaKY

Slaanesh: This Shit Will Fuck You Up http://www.youtube.com/watch?v=tHl5EO77Rn4 (ignore the shitty video)

Tentative Nurgle (not really squishy enough) What The Fuck Is Wrong With You http://www.youtube.com/watch?v=ln0aVbWzV6s&feature=related

Haven't found anything for Tzeentch yet, but This Is My Rifle (http://www.youtube.com/watch?v=5Ism2I3HCGU&feature=related) is PERFECT ImpGuard material.

And yes, I know about BoltThrower, and I'm not terribly fond of them.